1. Field of the Invention
The invention relates to a process for the preparation of hydrogen peroxide by the alkylanthraquinone technique More particularly, the invention is concerned with providing a process for obtaining concentrated aqueous hydrogen peroxide solutions with low contents of impurities.
The invention also relates to a plant for obtaining concentrated aqueous hydrogen peroxide solutions which are purified from impurities.
2. Discussion of the Background
In the organic synthesis of hydrogen peroxide by the alkylanthraquinone process it is well known (European Patent EP-Bl-0,032,338 in the name of Oxysynthese) to inject inorganic stabilisers at the oxidation stage with the aim of preventing the decomposition of the hydrogen peroxide produced. The stabilisers thus added pass into the extraction stage with the organic working solution containing the H.sub.2 O.sub.2. At this point an additional quantity of inorganic salts and/or acids acting as stabilisers via pH control and as corrosion inhibitors is generally added via the stream of water feeding the extraction column. These stabilisers and acidifiers are extracted in the aqueous phase with the H.sub.2 O.sub.2. The organic phase leaving the extraction unit, which is then recycled to the hydrogenation unit to recommence the production cycle, therefore no longer contains any stabiliser for H.sub.2 O.sub.2 and must therefore be subjected to an addition of fresh stabilisers before returning to the oxidation.
In the distillation unit, an additional quantity of stabilisers is also frequently added to the water employed to form the liquid reflux of the rectification column (U.S. Pat. No. 3,073,755 in the name of Laporte Chemicals).
Since the large majority of the stabilisers and corrosion inhibitors and acidifiers which enter the distillation unit are relatively nonvolatile when compared with H.sub.2 O.sub.2, they are encountered again in the purge with the impurities which are continuously removed from the distillation unit.